Abstract Heat capacity experiments are reported on the copper compounds Cu(CnH2n+1NH3)2Cl4 and Cu(CnH2n+1NH3)2Br4 with n varying from 1 to 5. A curve for the specific heat of the quadratic Heisenberg ferromagnet is produced ; however, the separation of the magnetic and lattice contributions has been a complicated problem. The resultant curve shows a broad maximum of Cmax/ R = 0.36 at kTmax/ J = 1.1. Very small λ-type anomalies, the heat content of which decreases with increasing n are found around kTc/J = 0.45.